I'll have to check on the LUN with another person. I was focused on the file groups as a way to avoid backing up all the data, so I overlooked filegroups as a way to temper/throttle the impact of a single large backup. This approach will also address some of the timing/process issues as I can backup at the appropriate time. Thanks very much!

I'll have a trial of Redgate Backup Pro on the server in the next couple of days, and hope that will also make managing multiple filegroup backups easier.